Photographic printing of cathode-ray tube screen structure

ABSTRACT

During the fabrication of a cathode-ray tube screen structure, a light field is projected through a photographic master, a correction lens and an optical filter incident upon a photosensitive layer. The filter is a relief image comprised of preformed, nonmetallic, light-absorbing particles having a mean diameter in the range of 5 to 50 millimicrons in a lighttransmitting binder. The filter has variations in light transmittance which produce predetermined variations in light intensity in the light filed tailored to the particular system.

United States Patent Inventor Harry Robert Frey Lancaster, Pa.

Appl No 844,852

Filed July 25, I969 Patented July I3, 1971 Assignee RCA Corporation PHOTOGRAPRIC PRINTING OF CATHODE-RAY TUBE SCREEN STRUCTURE 10 Claims, 4 Drawing Fig.

0.8. CI. 95/] R int. Cl. G031: 7/00, HOlj 1/62. HOlj 29/89 Field of Search 951i [56] Reference! C lted UNITED STATES PATENTS 3,448,667 6/1969 Smithgall a 9S/l Primary E1aminer-Samuel S4 Matthews Assistant Examiner- Kenneth C. Hutchinson Attorney-Glenn H. Bruestle ABSTRACT: During the fabrication of a cathode-ray tube screen structure, a light field is projected through a photographic master, a correction lens and an optical filter incident upon a photosensitive layer. The filter is a relief image corn prised of preformed, nonmetallic, light-absorbing particles having a mean diameter in the range of 5 to S0 millimicrons in a light-transmitting binder. The filter has variations in light transmittance which produce predetermined variations in light intensity in the light filed tailored to the particular system.

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IN V! {NI )R Harry R. Frey I ATTORNEY PHOTOGRAPHIC PRINTING OF CATHODE-RAY TUBE SCREEN STRUCTURE BACKGROUND OF THE INVENTION This invention relates to an improved photographic method for printing a screen structure for a cathode-ray tube, such as a color television picture tube.

A commercial picture tube for color television. or a color kinescope as it is sometimes called, is a cathode-ray tube which includes a viewing screen comprised generally of a multiplicity of red-emitting, green-emitting and blue-emitting phosphor elements. These elements are usually arranged on the inner surface of the faceplate panel of the picture tube in a regular cyclic array. In the shadow mask-type picture tube, the phosphor elements are usually dots arranged in groups of threes or triads, each triad having a red-emitting dot, a greenemitting dot and a blue-emitting dot. There are, of course, other geometric arrangements and shapes of phosphor elements for other cathode-ray tube types.

In order to produce a television picture with suitable resolution and color purity, the process for forming the phosphor elements must be capable of producing a very large number of phosphor elements of relatively small and uniform size which are accurately positioned with respect to one another, The complexity of the problem is demonstrated by the fact that the viewing screen for a shadow mask-type kinescope may include more than a million phosphor dots, each of about 12 mils in diameter.

In one preferred process for printing phosphor elements for a shadow mask-type viewing screen, the inner surface of the faceplate panel is coated with a mixture of phosphor particles and a photosensitive binder. A light field is projected from a point source upon the coating through the shadow mask ofthe tube, which mask functions as a photographic master or negative in the process. The exposed coating is subsequently developed to produce phosphor elements of the first phosphor; for example, blue-emitting phosphor dots. The process is repeated for the green-emitting phosphor elements and again for the red-emitting phosphor elements using the same shadow mask as a photographic master. The point source is appropriately offset during the exposure steps so as to produce phosphor elements which are displaced from one another to form the prescribed triads.

It is known that the size of the phosphor elements is deter mined in part by the size of the holes in the shadow mask, by the spacing of the shadow mask from the phosphor-photosensitive binder coating, and by the amount of light exposure of the coating. With respect to this last factor, the greater the exposure, the larger will be the phosphor elements formed. Hence, the exposure is carefully controlled with respect to light intensity and with respect to duration ofexposure. In addition, the difference in light intensity between the edge and the center of the projected light field (due to the geometry of the optical system) is compensated for by geometrically arrayed coatings of opaque material (usually circular bands of rhodium metal) on one or more optical elements in the optical system.

There are also variations in light intensity across the light field due to random or chance variations, irregularities, or distortions in the optical system. The usual commercial optical system used in manufacturing viewing screens for kinescopes is referred to as a lighthouse. The lighthouse includes an ultraviolet lamp in a light box which has a single window in the form of a light pipe, such as a quartz rod, that is tapered to a small cross-sectional area of controlled shape at its terminal end. The terminal end functions as the point source of light from which the light field is projected first through an optical refracting lens or lenses, then through the photographic master and then incident a light sensitive layer. The light field has both bright spots and dim spots which are peculiar to each particular lighthouse. These intensity variations in the light field may be caused by peculiarities in the ultraviolet lamp, in

its positioning with respect to the quartz rod, l'y imper ections in the quartz rod, or by imperfections in the optical character of the terminal end of the rod. singularities in the refracting lens or lenses may also produce dim and/or bright spots in the light field. These variations in intensity in the light field from whatever source are carried over to the light-sensitive coating where, during exposure, they produce phosphor elements which may be larger or smaller than other phosphor elements on the same viewing screen. Such variations in phosphor element size effectively reduce the operating tolerances of the tube and, in its extreme, may be cause color impurity in the viewed television picture.

It has been proposed in US. Pat. No. 3,448,667 to H. E. Smithgall to insert into the path of the light field, an optical filter coating comprised of silver particles in a binder. The transmission characteristic of the filter is the negative pattern of the localized bright spots in the central portion of the light field. In practice, this optical filter coating is produced by exposing a silver halide emulsion coating to the light field in the exact position in which it is to be used in the lighthouse. The exposed coating is then developed, producing a layer of silver particles in a binder, While such a process produces usable filters, nevertheless the metallic silver particles, which are the active part of the filter, tend to grow to sizes that are so large as to produce scattering of light from the light field. Also, the usable silver halide emulsions have a small grain size and therefore a high contrast characteristic with a gamma greater than I and usually about 3 to 7. This restricts the useful expo sure range for making the filter within very narrow limits, since it is desired to produce a sufficient number of steps in the gray scale in the final filter. As a practical matter, a photosensitive layer having a gamma of about 1.0 is preferred.

SUMMARY OF THE INVENTION In the novel method, a light field is projected through a photographic master toward a photosensitive layer as in the prior art. The light field is also passed through a filter comprised of preformed, nonmetallic, light-absorbing particles having a mean diameter in the range of 5 to 50 millimicrons in a light-transmitting binder. The filter has variations in light transmittance which produce predetermined variations in light intensity in the light field tailored to the particular system.

In one embodiment of the novel method, the transmittance of the filter is inverse to the light intensity in the light field; that is, the filter is less transmitting to the brighter portions of the light field and more transmitting to the dimmer portions of the light field. The efi'ect of this filter is to compensate for part or all of the light intensity variations in the light field by reducing the brightness of the brighter portions of the light field. In another embodiment, the transmittance of the filter is graded to provide in the light field brighter and dimmer regions according to a predetermined design.

The filter in its preferred forms consists essentially of finely divided, preformed, lightabsorbing material particles of carbon having a mean particle size in the range of about 5 to 50 millimicrons, and preferably channel black particles having a mean particle size in the range of 9 to 29 millimicrons. An advantage of the novel method is that very little light is scattered from the light field by the finely divided, preformed, nonmetallic particles. While the reason is not understood, it is believed the mean diameter of the particles is smaller and more uniform than previously used silver particles derived from a silver halide emulsion. In addition, the method is reliable and long lived because the particles-binder combination is stable to ultraviolet and to other radiation over extended periods of use.

The novel method may include the steps of preparing the above-described filter. The filter may be prepared by coating a support with a photosensitive composition including preformed, nonmetallic, light-absorbing particles and the light-transmitting binder therefor, Then, the coated support is positioned in the optical system in which it is to be used. The positioned coating is exposed to the light field for a period of time sufficient to produce, in incremental areas of the coating, upon subsequent development, predetermined variations in light transmittance. Then, the coating is developed to produce the filter layer.

The nonmetallic particles are formed and stabilized in size prior to preparing the filter. As a result, the particles in the filter are of a small, substantially uniform, nonscattering size. The photosensitive coating has a gamma near the optimum of L0, thereby providing the desired grey scale in the filter. By using the light field itself to produce the filter, the positioning and brightness of incremental areas of the light field are accurately plotted in the filter. After the filter has been so prepared, it may be placed back into the same optical system in the same position in which it was exposed so that the variations in the filter are in substantial registration with the variations in brightness in the light field.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially broken away elevational view of a lighthouse comprising an optical assembly including a filter on the surface of one lens. The lighthouse has a faceplate panel thereon in position for practicing one form of the novel method.

FIG. 2 is a partially broken away elevational view of another lens assembly for the lighthouse of FIG. 1. The assembly includes a filter on the surface of another lens.

FIG. 3 is a partially broken away elevational view of another lens assembly for the lighthouse of FIG. I. The assembly includes a filter on the surface of a separate optical element from the lenses of the assembly.

FIG. 4 is a sectional elevational view ofa tank in the process of developing a filter according to one feature of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The novel method may be practiced in the lighthouse illustrated in FIG. I. The lighthouse is comprised ofa light box 21 and a panel support 23 held in position by bolts (not shown) with respect to one another on a base 25 which in turn is supported at the desired angle by legs 27.

The light box is a cylindrical cup-shaped casting closed at one end by an integral end wall 29. The other end of the light box 21 is closed by a plate 3! which fits in a circular recess 33 in the light box 21. The plate 3] has a central hole therein through which a light pipe 35 (referred to as a collimator in the tube making art) in the form of a tapered glass rod extends. The narrow end 47 of the light pipe 35 extends slightly beyond the plate 31 and constitutes a point source of light for the lighthouse. The wider end 39 of the light pipe 35 is held in position by a bracket 41 opposite a lamp 43 within the light box 2 l. A light reflector 45 is positioned behind the lamp 43.

A lens assembly SI is mounted on a lens assembly support ring 53 and stand off spacers 55 with bolts 57. The support ring is clamped in position between the light box 21 and the panel support 23. The lens assembly is comprised ofa correction lens 6! and a wedge lens 63 held and spaced from each other by a separator ring 65, an upper clamp 67 and a lower clamp 69. The upper surface of the wedge lens 63 has thereon an optical filter 71. The filter 7! is in the form ofa reliefimage comprised of preformed carbon particles (mean diameter about millimicrons) in gelatin or other clear colorless binder. The filter 7l varies in thickness up to about 3,000 angstroms thick. This is about a half-wavelength for yellow light. Because of its thickness, an observer may see interference patterns in the filter, which patterns have been found not to interfere with the novel method. These interference patterns may be eliminated by applying over the filter 71 an overcoating of clear colorless gelatin or a similar substance.

The filter has essentially a neutral gray transmittance varying only in the intensity of grayness. The intensity of grayness varies from point-to-point so that point-to-point variations in brightness in the light field are reduced. That is, the filter has variations in transmittance which are in registration with and inverse to the variations in intensity in the light field passing through the filter. These variations in transmittance reduce the light intensity variation in the light field.

There may be many sources causing variations in light intensity in the optical system. These may come from the lamp 43, its position with respect to the light pipe 35, from the light pipe 35 particularly the narrow emitting end 37, from the wedge lens 63, from the reflector 45, or its position with respect to the light pipe 35. Any singularity such as an imperfection in these optical elements either internal or surface may have the effect of producing dimmer or brighter positions in the light fieId.

The filter may include other compensations besides those for point-topoint intensity variations. For example, the filter may include compensations for the geometry of the system, such as a center-to-edge variation in light intensity due to the spreading of the light. Also, the filter may be designed to impart predetermined variations in light intensity in the light field. Thus, the filter may be used to produce a more uniform light field or a field with predetermined light intensity variations. The compensations may be achieved solely with the above described filter or in combination with other types of filters, such as metal opaquing bands or one or more of the optical elements.

In one mode for operating the lighthouse of FIG. I, a faceplate panel 73 having a layer 75 comprised of light-sensitive binder and phosphor particles on the inner surface thereof and a mask assembly 77 mounted therein is placed in position on the panel support 23 as shown in FIG. I. A light field from the narrow end 37 of the light pipe 35 passes upwardly through the wedge lens 63, the filter 71 and the correction lens 61. In passing through the filter 71, the point-to-point intensity variations in the light field are reduced by the selected transmittance in the filter. The light field then passes upwardly through the apertures 79 in the mask assembly 77. The light passing through the apertures falls incident upon the phosphor layer 75 exposing the light sensitive binder, thereby changing its solubility characteristics. Since the light intensity is more uniform across the light filed, the binder is more uniformly exposed. After cxposure, usually of the order of 5 to 25 minutes, the light is eclipsed, the panel 73 is removed from the support, the mask assembly 77 is removed from the panel 73, and the phosphor layer 75 is developed to produce the desired image on the panel 73.

The filter 7] may reside on the top surface of the compensating lens 6t as shown in FIG. 2 or may reside on the top surface of a separate optical element 81 as shown in FIG. 3 wherein it is positioned between the compensating lens 61 and the wedge lens 63, instead of on the wedge lens 63 as shown in FIG. I. In any of the foregoing alternatives, the assembly 51 may be mounted as shown in FIG. I. In still another alternative. the separate optical element 8! with the filter 71 thereon may be mounted near the mask assembly 77 as shown by the dotted box 83 in FIG. 1. Also, the functions of the correction lens 61 and the wedge lens 63 may be combined into a single lens.

The filter 71 shown in FIG. I may be prepared by the following process. The upper surface of the wedge lens 63 which is about 1 1% inches in diameter is first cleansed, rinsed in an 0.05 weight percent aqueous gelatin solution and then dried. The surface is then rinsed in warm (50 C.) deionized water and again dried, leaving a thin gelatin precoating on the surface. The precoated surface is coated with a light-sensitive composition comprised of very fine particle carbon in a sensitized gelatin binder. The preferred carbon is a channel black called Black Pearls 607 marketed by Cabot Corporation, Boston, Mass. This material has a means particle diameter of about 9 millimicrons by electron micrograph (E.M.) study.

One suitable coating composition contains about grams Black Pearls 607, about 12 grams Marasperse CB dispersing .rgent, about 42 grams Brij 35 SP wetting agent, about 1,380 rams gelatin, about 10,000 grams deionized water, about 37 grams Hardener 03 (4,4'-diazidostilbene-2,2'-disulfonic acid sodium salt) which is a sensitizer for the gelatin. and about 300 grams ammonium hydroxide solution. A warm (40 C.) quantity (about 150 cc) of this liquid composition is poured upon the slowly rotating lens. The lens is then spun at about 60 rpm. until the composition has spread to a uniform layer about 1 mil thick and then gelled (about 3 minutes). After cooling and drying, the coated wedge lens 63 is placed in the lens assembly 51 in the position in which it is to be used. A light field is projected from the light pipe 35 incident upon the coating for about 2-5 minutes at about 45 foot candles. The optimum exposure is determined empirically.

The exposed coated lens is then removed from the lighthouse and placed in a dilute (about 0.01 to 1.0 weight percent) solution of potassium alum for about 5 minutes at room temperature and then placed in a laminar flow trough, such as the trough 83 shown in FIG. 4. The lens 61 is placed on a holder 85 with the exposed coating 'l'la faced down. The trough 83 is filled with flowing warm (50 C.) water 87 which is fed in through a tube 89 and overflows through an orifice 91. Laminar flow is achieved by providing a metal wool baffle 93 upstream from the lens 61 and a solid baffle 95 having a slot at the bottom thereof downstream of the lens 61. The water is permitted to flow slowly for about 30 minutes through the trough 83 being careful not to disturb the system. During developing, the unexposed coating slowly dissolves leaving the exposed material in position on the lens. The temperature of the water flowing through tube 89 is then lowered to C., and the solid baffle 95 is removed. When the temperature of the water leaving orifice 91 is below C., the lens is removed from the trough. After developing, the lens is dried and is ready for use. In use, the lens is positioned in the identical position in which the coating was exposed during the preparation of the filter 71.

GENERAL CONSIDERATIONS Other photosensitive coatings may be used in place of the gelatin-carbon mixture described above. For example, one may use finely divided preformed particles of any dark colored nonmetallic substance which is otherwise chemically stable. Channel blacks and furnace blacks with mean particle diameter (E.M.) in the range of about 5 to 50 millimicrons can be used. Channel blacks having a mean particle diameter in the range of 9 to 29 millimicrons are preferred. Other dark colored substances that may be used are dark colored oxides of manganese, cobalt and nickel. it is preferred that the photosensitive coating have a spectral absorptivity that is fairly closely matched to the spectral sensitivity of the light sensitive layer which is later to be exposed through the filter. Also, it is preferred that the light-absorbing particles in the filter be as small as possible.

The preferred coating material consists essentially of a gelatin binder, fine particle carbon pigment, wetting and dispersing agents, an organic photosensitizing agent, and water as a solvent. Sensitized gelatin is the preferred photobinder because it gels during the last stage of development preventing mechanical handling damage to the soft relief image. But, other photobinders may be used. To minimize light scattering characteristics of a filter, the means particle diameter must be extremely small; in the range of 5 to 50 millimicrons. An important feature of the invention is the use of nonmetallic particles whose size is determined before and not during and/or after the filter is fabricated. The binder and the pigment are the essential parts of the final filter; other materials are required only in filter fabrication and should have low light absorption properties or should be added in the lowest practicable concentrations. Wetting and dispersing agents are added to improve adherence of the filter to the support and to produce smoother more uniform coatings. Marasperse" dispersing agents are marketed by American Can Co., N. Y.,

Gelatin (weight percent) s 1-25 Carbon/gelatin ratio 0 001-0. 5 Disporsing agent/carbon ratio s 0ll 0 Wetting agent/carbon ratio 0. 01-1 0 Photosensitizing agent/gelatin ratio s s 0 005-0 20 Ammonium hydroxide to maintain pH 8.5-9. 5. Water, remainder.

The light sensitive material may be applied to a transparent substrate in any manner which provides a relatively uniform, excessively thick dried layer. These methods include dip coating, flow coating, and spin coating. Coating thickness variation is not critical when organic photosensitizers are incorporated in the formulation.

Photoexposure of the dried photosensitive coating is accomplished preferably in the optical apparatus in which the finished filter is to be used. The light source of the apparatus must emit actinic light. The filter is then replaced in the apparatus after processing in the same orientation in which it was exposed since density variations printed in the filtermatch incident light intensity variations. Exposure of the photosensitive coating must be accomplished through the transparent substrate thereby first hardening the coating material adjacent to the substrate on which it resides. As exposure continues, hardening progresses into the photosensitive layer forming a continuous tone relief image.

Development is completed in two steps. A short soak in cold 2S C.) potassium alum solution is necessary to insolublize anionic dispersing agents and partially harden the gelatin. Unexposed coating material is then washed away in a threecompartment tank 83 shown in FIG. 4 filled with gently flowing warm (50 C.) water. The filter plate is placed in the center compartment with the coating surface down. Water injected into the bottom of the left side of the tank flows through a perforated baffle, down across the filter plate, and exits through the right compartment. When all of the unexposed coating material has been removed, the water temperature is decreased 20" C.) to gel the soft filter surface before removing the filter from the tank 03. The cold filter is carefully removed and dried.

The process of fabrication with carbon-gelatin compositions provides filters not attainable before, which will automatically correct for bright spots or dark spots in an optical field. Grain size of the particles of the filter is small enough not to distort an image significantly by light scattering, and filter uniformity is improved. By comparison nearly all photographic silver emulsions have excessively large grain size. Lippmann-type silver emulsions have small grain size, but cannot be developed sufficiently uniformly to a continuous tone grey scale.

The novel method may be used to prepare any screen structure by a photographic process. Dot screens and line screens are examples. By "screen structure" is meant any component part of a cathode-ray tube target; for example a luminescent layer, or a light-absorbing layer. The novel process may be used to expose a layer comprised of photobinder-particles mixture, or to expose a clear photoresist and then phosphor particles or light absorbing particles may be deposited on the exposed areas. In the example, a phosphor screen structure is deposited directly by exposing a layer comprised of phosphor particles mixed with a photobinder. An alternative method is to expose a layer of clear photobinder, then deposit phosphor particles thereon and then remove more soluble portions of the photobinder and the overlying phosphor particles.

Another method for preparing a phosphor screen structure is to expose a layer of clear photobinder, remove the more soluble portions thereof, then deposit phosphor particles thereover and finally remove the less soluble portions of the photobinder layer with the phosphor particles thereon and leaving phosphor particles in the portions previously occupied by the more soluble portions of the photobinder layer. The novel process may also be used to produce nonluminescent screen structures, such as a light absorbing matrix. An example of this is to expose a clear photobinder layer to a light image, remove the more soluble portions thereof then deposit light absorbing particles such as fine'particlc graphite thereover, then remove the less soluble portions of the photobinder layer with the light-absorbing particles thereon and leaving the light-absorbing particles in the portions previously occupied by the more soluble portions of the photobinder layer. Thus, the novel method may be used to prepare either luminescent or nonluminescent screen structures by a photographic method.

lclaim:

I. In a photographic method for printing a screen structure for a cathode-ray tube, the steps comprising A. projecting a light field toward a photosensitive surface,

B. passing said light field through a filter comprised of finely divided preformed, nonmetallic, light-absorbing particles having a mean diameter in the range of to 50 mil limicrons, said filter having variations in light trans mittance, whereby to produce predetermined variations in light intensity in said light field,

C. passing said light field through a photographic master.

D. and further projecting said light image incident upon said photosensitive surface.

2. The method of claim I wherein said filter includes a layer consisting essentially of finely divided carbon particles in a light-transmitting binder, and the light transmittance variations thereof were derived from said light field.

3. The method of claim 2 wherein said filter consists essentially of finely divided particles of channel black in a light transmitting binder, said particles having a means diameter in the range of about 9 to 29 millimicrons.

4. in the photographic method defined in claim 1 for printing a screen structure for a shadow mask-type color itinescope comprising a. projecting from a substantially point source a light field having variations in light intensity thereacross,

b. projecting said light field through said filter,

c. projecting said filtered light through the shadow mask for said kinescope, whereby to produce a filtered light image,

d. further projecting said filtered light image incident upon a photosensitive layer which is supported upon the inner surface of the faceplate of said kinescope. whereby to produce in said layer selected regions of material which are more soluble and other selected regions of material which are less soluble in a particular solvent,

e. and then removing those selected regions which are more soluble while retaining those regions which are less soluble.

5. The method defined in claim 4 wherein said photosensi' tive layer includes particles of phosphor to be printed thereon, and said retained regions define the screen structure to be printed.

6. The method defined in claim 4 wherein said photosensitive layer is substantially free of particles to be printed, and including the further steps of:

f. depositing particles ofa light-absorbing material in the regions from which said more soluble material has been removed,

g. and then removing said less soluble material while retaining said light-absorbing material in the regions from which soluble material has been removed.

7. The method defined in claim 4 wherein said photosensitive layer is substantially free of particles to be printed, and in cluding the further s te s of: I

f. depositing partic es of a luminescent material in the regions from which said more soluble material has been removed g. and then removing said less soluble material while retaining said luminescent material in the regions from which soluble material has been removed.

8. The method defined in claim 4 including, prior to step (A the defined for producing said filter layer comprising i. coating a support for said filter layer with a photosensitive composition including preformed, nonmetallic, light-absorbing particles and a binder therefor, said particles having a mean particle diameter in the range of about 5 to 50 millimicrons,

ii. positioning said support in said optical system in the position in which it is to be used, said coating being on a surface remote from said point source,

iiiv exposing said coating to said light field in said position for a period to time sufficient to produce in incremental areas of said coating, upon subsequent development, variations in light transmittance which are inverse to the light intensity of the corresponding incremental areas of said light field,

iv. and then developing said coating to produce said filter layer.

9. The method defined in claim 8 wherein said light-absorbing particles recited in step (i) are carbon particles.

It]. The method defined in claim 8 wherein said light-absorbing particles recited in step (i) are channel black carbon having a mean particle diameter in the range of about 9 to 29 millimicrons. 

1. In a photographic method for printing a screen structure for a cathode-ray tube, the steps comprising A. projecting a light field toward a photosensitive surface, B. passing said light field through a filter comprised of finely divided preformed, nonmetallic, light-absorbing particles having a mean diameter in the range of 5 to 50 millimicrons, said filter having variations in light transmittance, whereby to produce predetermined variations in light intensity in said light field, C. passing said light field through a photographic master, D. and further projecting said light image incident upon said photosensitive surface.
 2. The method of claim 1 wherein said filter includes a layer consisting essentially of finely divided carbon particles in a light-transmitting binder, and the light transmittance variations thereof were derived from said light field.
 3. The method of claim 2 wherein said filter consists essentially of finely divided particles of channel black in a light-transmitting binder, said particles having a means diameter in the range of about 9 to 29 millimicrons.
 4. In the photographic method defined in claim 1 for printing a screen structure for a shadow mask-type color kinescope comprising a. projecting from a substantially point source a light field having variations in light intensity thereacross, b. projecting said light field through said filter, c. projecting said filtered light through the shadow mask for said kinescope, whereby to produce a filtered light image, d. further projecting said filtered light image incident upon a photosensitive layer which is supported upon the inner surface of the faceplate of said kinescope, whereby to produce in said layer selected regions of material which are more soluble and other selected regions of material which are less soluble in a particular solvent, e. and then removing those selected regions which are more soluble while retaining those regions which are less soluble.
 5. The method defined in claim 4 wherein said photosensitive layer includes particles of phosphor to be printed thereon, and said retained regions define the screen structure to be printed.
 6. The method defined in claim 4 wherein said photosensitive layer is substantially free of particles to be printed, and including the further steps of: f. depositing particles of a light-absorbing material in the regions from which said more soluble material has been removed, g. and then removing said less soluble material while retaining said light-absorbing material in the regions from which soluble material has been removed.
 7. The method defined in claim 4 wherein said photosensitive layer is substantially free of particles to be printed, and including the further steps of: f. depositing particles of a luminescent material in the regions from which said more soluble material has been removed g. and then removing said less soluble material while retaining said luminescent material in the regions from which soluble material has been removed.
 8. The method defined in claim 4 including, prior to step (A), the defined for producing said filter layer comprising i. coating a support for said filter layer with a photosensitive composition including preformed, nonmetallic, light-absorbing particles and a binder therefor, said particles having a mean particle diameter in the range of about 5 to 50 millimicrons, ii. positioning said support in said optical system in the position in which it is to be used, said coating being on a surface remote from said point source, iii. exposing said coating to said light field in said position for a period to time sufficient to produce in incremental areas of said coating, upon subsequent development, variations in light transmittance which are inverse to the light intensity of the corresponding incremental areas of said light field, iv. and then developing said coating to produce said filter layer.
 9. The method defined in claim 8 wherein said light-absorbing particles recited in step (i) are carbon particles.
 10. The method defined in claim 8 wherein said light-absorbing particles recited in step (i) are channel black carbon having a mean particle diameter in the range of about 9 to 29 millimicrons. 